So, you go to sleep at night dreaming of the Louis Vuitton Murakami Multicolor bag. You know, the white canvas bag adorned with brightly colored trademark LV’s, gold hardware and tan leather detailing. Apologies, but your chances of acquiring this bag are slim. The LV Murakami bag is in high demand and short supply, meaning you have to tack your name onto a hefty waiting list.

There is, however, an alternative to signing the waiting list and crossing your fingers: Ebay. A search for the LV Murakami bag turns up roughly 150 results. There it is, the bag of your dreams; but how do you trust an anonymous cyberseller?

There are two kinds of designer bags on Ebay: those described as authentic and those that are “designer inspired” or “designer style.” The inspired and style bags are obvious fakes, and the seller admits it up front. It’s the bag marketed as authentic that raises questions.

To get an idea of the going rate for designer bags on Ebay, an orange leather Birkin 25 was recently going for more than $10,000 with three days left for bidding. A small clutch from the Murakami collection recently sold for $152. The same bag is available from www.eluxury.com, a registered Louis Vuitton outlet, for $475.

When LV Murakami sellers were questioned about the authenticity of their bags and how exactly they could prove it, the results were hardly convincing. “It’s hard to tell you how I know. It takes years of expertise.”

Another seller unable to prove the authenticity said, “I don’t have a receipt as I bought it from another on Ebay. I have taken it to an LV boutique and it has been authenticated by the manager. I don’t have any proof, just verbal acknowledgment from her.”

Finally a seller offered evidence of authenticity. “I can send a copy of the receipt.” Well, that sounds sufficient, doesn’t it?

But, the big question is: Will my bag be legit?

“I wouldn’t personally buy a bag on Ebay. I’ve gotten so many phone calls from women who paid thousands of dollars and then found out the bag was fake,” said Joseph C. Gioconda, a partner at Kirkland and Ellis LLP and attorney for Hermes.

After representing the French designer for seven years, Gioconda has seen his share of imitation bags and the disappointment they carry with them.

His advice? “Put yourself on the waiting list and wait it out.”

Although Ebay doesn’t officially permit counterfeit merchandise on its Web site, sellers are not required to prove authenticity before posting their goods. Ebay suggests, but does not require, authentication by an independent expert before listing an item, but most of the time the seller is the one shouting, “It’s AUTHENTIC!” Rarely is an experienced professional referenced.

Ebay will act if an expert says an item on the Web site is not accurately represented depending on the situation. Look for authentication by an expert on the listing, and if you buy a bag and then question the integrity, take it to an authorized retailer.

Being able to tell the difference between authentic and imitation bags is the second step in a two-part process. You must first know the difference between counterfeit and knock-off bags. Gioconda explains that counterfeit bags have a registered trademark similar to the authentic trademark so that they seem indistinguishable from the original. Knock-offs look identical to the original, but the name is omitted. First, look for a trademark identical to that found on the real bag. If it’s not there or is slightly different, the bag is a knock-off.

More examination is required if the bag looks remarkably similar to the original.

The photos shown on Ebay are often file photos, which means they are not pictures of the actual bag being auctioned. Furthermore, the pictures aren’t always clear enough to see the details, warns Julie Bennett, associate professor of fashion at Stephens College. She said it is very difficult to tell the differences online, and that it is best to see the bag in person and look at the lining.

“The person with the real stuff can tell the difference,” said Sharon Haver, founder and style director of www.FocusOnStyle.com, an online fashion magazine. “The easiest way to tell is in the hardware.” The Gucci buckle, Louis Vuitton zipper and Birkin strap are examples of where the difference between genuine and “inspired” bags are most obvious.

Bennett points out more general materials to examine, such as the quality of leather, brass studding and stitching. For example, the stitching on a Prada bag tends to be slightly angled, she said. The key to spotting the well-executed fake bags is in the minute details.

Find out if the purse you’ve got your eye on comes with a certificate of authenticity. In order to protect themselves and their customers from fakes, designers recently started putting certificates inside their purses.

The cost of a bag on Ebay should be comparable to the price set by the designer. Check with a retailer or www.eluxury.com.